1. Field of the Invention
The present invention relates to a communication system, and more particularly to an apparatus and method for coding in a communication system.
2. Description of the Related Art
The most fundamental issue in communication is how to efficiently and reliably transmit data over a channel. In a next-generation communication system that has been actively studied in recent years, a high-speed communication system is required, which departs from an early voice-only service, and can process and transmit a variety of information, such as images, wireless data, and the like. Therefore, it is essential to improve system efficiency by using a channel coding technique appropriate for the system.
Channel codes used for channel coding in a communication system include a Low Density Parity Check (LDPC) code.
The LDPC code is a coding scheme appropriate for a 4th generation mobile communication system because it has superior performance to that of a turbo code, has lower decoding complexity than that of the turbo code, and allows fast processing.
Such an LDPC code, which was first introduced by Gallager in 1962, is a linear block code defined by a sparse parity check matrix H, the elements of which are mostly “0”. The LDPC code was out of the public's sight and mind because, in view of the state of the art at that time, it was too complex to be implemented. However, MacKay and Neal rediscovered the LDPC code, and demonstrated its excellent performance by using a simple probabilistic decoding method proposed by Gallager.
The LDPC code is defined by a parity check matrix in which most elements have a value of 0, and a small minority of elements other than the zero elements have a value of 1. That is, a parity check matrix of the LDPC code has a very small number of weights, and thus the LDPC code can be decoded through iterative decoding even in the case of a block code with a relatively long length. If the block length of the block code continues to increase, the LDPC code shows performance approaching the channel capacity limit of the Shannon's channel coding theorem. However, one obstacle to implementing the LDPC code is coding complexity. The coding is performed by matrix multiplication, which causes a problem in that coding complexity increases in proportion to the square of code length.